The present invention relates generally to semiconductor packaging. More particularly, a packaging arrangement that utilizes bonding wires as external contacts is described.
In the semiconductor industry, there are continuous pressures to reduce the cost of packaging integrated circuits. To accomplish this, a wide variety of package designs and assembly methods have been developed. One of the currently used techniques for producing integrated circuit (IC) packages is referred to as flip chip packaging. Flip chip packages are typically produced by attaching solder balls or solder columns to input/output terminal pads on the top surface of an integrated circuit die. The solder balls or columns form interconnecting contacts that are used to connect the die to other electrical elements such as a printed circuit board. During the assembly of the flip chip package onto a substrate such as a printed circuit board, the integrated circuit die is flipped upside down such that the solder balls or columns face the substrate and the die is then attached to the substrate . FIGS. 1 is a cross sectional view illustrating a typical flip chip package, designated by reference numeral 10, that is attached to a substrate material such as printed circuit board 12.
As shown in FIG. 1, flip chip package 10 includes an integrated circuit die 14 and a plurality of solder ball or solder column interconnecting contacts 16. Interconnecting contacts 16 are attached to associated input/output terminal pads 18 formed on a surface 20 of integrated circuit die 14. Interconnecting contacts 16 are used to electrically connect integrated circuit die 14 to a substrate such as printed circuit board 12. Because interconnecting contacts 16 are rigid columns or solder balls, these interconnecting contacts form rigid connections between integrated circuit die 14 and printed circuit board 12. These rigid connections are susceptible to cracking or separation due to vibration and/or thermo-mechanical stresses placed on the finished printed circuit board. In order to improve the reliability of the mechanical connection between the flip chip package 10 and the printed circuit board 12, an epoxy material 22 or other such adhesive material is used to underfill flip chip package 10 and adhere package 10 to printed circuit board 12 after the package is assembled onto the printed circuit board. This underfill process is an extra step in the assembly process and adds to the cost of assembling the system using this type of flip chip package. Indeed, one of the greatest drawbacks of current flip chip technology is that the production and assembly costs are too high in many circumstances. Additionally, as die sizes are reduced and die complexity is increases, there are ongoing needs to create finer pitch interconnects. Solder balls 16 tend to be relatively large and thus in some circumstances the die size reductions are limited by external interconnect constraints. Thus, simpler and lower cost packaging techniques that utilize proven technologies and meet the needs of current integrated circuits would be desirable.
One well established packaging technology is wire bonding. Recently, there have been some attempts to utilize wire bonding techniques in the formation of contacts or flip chip and/or chip scale packages. By way of example, U.S. Pat. No. 5,496,775 to Brooks contemplates forming towers of gold ball bonds on top of one another to form a contact. The towers are then partially backfilled, which helps hold them in place. However, it is relatively difficult to build reliable ball bond towers without damaging the underlying bond pads. In commonly assigned, co-pending application Ser. No. 08/998,442 filed Dec. 24, 1997 (which is incorporated herein by reference), Kelkar et al. take another approach which contemplates the use of wire bond loops as contacts. These loops may also be backfilled for support. Although this approach works well, additional contact forming techniques are always desirable.